The epidermal growth factor receptor (EGFR) is the prototypical type-I receptor tyrosine kinase and the first member of the ERBB family of receptors to be identified (Coussens et al., 1985; Kraus et al., 1989; Carpenter & Wahl, 1990; Plowman et al., 1990; Plowman et al., 1993; Gullick, 1998). It is a member of the ERBB family of receptor tyrosine kinases, and is also known as HER1 and ERBB1. Other members of the family include HER2/NEU/ERBB2, HER3/ERBB3, and HER4/ERBB4.
The ERBB receptors have similar structures, with extracellular ligand-binding domains, a single membrane-spanning region, and a cytoplasmic protein tyrosine kinase domain. Under normal physiological conditions, the activity of the ERBB receptors is controlled by the availability of their ligands, which are members of the EGF-related growth factor family. The binding of EGF to EGFR causes dimerization of the receptor, leading to autophosphorylation and the recruitment of various molecules associated with signal transduction. Ligand binding to EGFR also results in the formation of heterodimers of EGFR and other members of the ERBB family.
EGFR, like other ERBB receptors, is required for normal mammalian development (Threadgill et al., 1995). However, inappropriate expression and/or activity of the ERBB receptors has been associated with various tumors, including tumors of the breast, colon, lung, ovary, and head and neck, and also in glioma (Rasheed et al., 1999; Wong et al., 1992; Moscatello et al., 1995). For example, there is some indication that the activity of heterodimers between EGFR and other ERBB family members (for example, ERBB2) is associated with cellular transformation and poor prognosis. Additionally, ERBB2 must heterodimerize with another ERBB family member in order to become activated, and given the role that ERBB2 appears to play in metastatic breast cancer, an ability to modulate the formation of ERBB2-containing heterodimers would be a possible strategy for treating and/or preventing this disease.
As such, there is considerable effort in the medical community to identify modulators of the ERBB family. Several such modulators are in clinical development or are already available, including the anti-EGFR antibodies ERBITUX® (cetuximab; ImClone Systems Incorporated, New York, N.Y., United States of America) and ABX-EGF (panitumumab; Abgenix, Inc., Fremont, Calif., United States of America). HERCEPTIN® (trastuzumab; Genentech, Inc., South San Francisco, Calif., United States of America) is a monoclonal antibody directed against ERBB2/HER2 that has been approved by the Food and Drug Administration for the treatment of ERBB2/HER2 positive metastatic breast cancer. Each of these antibodies is believed to modulate receptor activity by blocking ligand binding and/or enhancing endocytosis of the receptor, thus limiting its availability to become activated by ligand binding.
Small molecule inhibitors of EGFR, including IRESSA® (gefitinib/ZD1839; AstraZeneca PLC, London, United Kingdom) and TARCEVA™ (erlotinib; (OSI)™ Pharmaceuticals, Melville, N.Y., United States of America), have also been produced. These small molecules are thought to inhibit the kinase activity of EGFR. However, they are likely to be non-specific for EGFR, with significant activity on other tyrosine kinases.
Despite these advances, current methods for modulating EGFR heterodimer activity are hindered by their reliance on modulators that also modulate the activity of homodimers of the ERBB family and/or other tyrosine kinases. Ideally, a modulator should modulate the activity of EGFR heterodimers without affecting the activity of homodimeric forms of the ERBB family or ERBB family heterodimers that do not include EGFR. Thus, there exists a long-felt need in the art for modulators that are specific for heterodimers that contain EGFR.
To meet this need, the presently disclosed subject matter provides in some embodiments a method for identifying modulators that specifically bind to EGFR heterodimers. Such modulators are useful for treating disorders associated with undesirable EGFR heterodimer activity, among other applications.